1. Field of the Invention
This invention relates to a photopolymerizable composition, and more particularly to a photopolymerizable composition giving a color when it is exposed to a light.
2. Description of Prior Art
When a photopolymerizable composition is used in the field of image forming materials such as a photoresist and a photographic paper, it is very convenient that exposed area is visually distinguishable. Such a function is called printing-out or print-out.
Th photosensitive material having the above printout function is advantageously used. In more detail, when a plate-processing operator once stops his exposure operations for simultaneously exposing many photosensitive printing plates and afterwards continues his exposure operations, he is able to visually distinguish which plates are already exposed. Further, when a sheet of a large plate is to be exposed many times as in the photocomposing method in the preparation of lithographic printing plates, operators are able to immediately confirm as to what area is exposed so that failures such as double printing can be prevented.
Accordingly, a printing-out composition or system is incorporated in many photosensitive materials used in photoresist and photosensitive printing plates at present so that an exposed area can be easily distinguished before development.
Examples of the printing-out systems include systems of photo-oxidizing various leuco compounds to the corresponding dyes using an organic polyhalogen compound or other photo-oxidizing agent (see Photo. Sci. Eng., 5, 98-103(19610) and U.S. Pat. No. 3,042,515). These known printing-out systems give printed-out images having excellent contrast, but have a drawback in that there is difficulty in stability in storage.
The use of a combination of a lactone compound and a compound generating an acid by irradiation of light as the printing-out system is disclosed in Japanese Patent Publication No. 49(1974)-6212 and Japanese Patent Provisional Publication Nos. 50(1975)-128228 and 50(1975)-80120. However, a printed-out image obtained in the system is not considered to be satisfactory with respect to contrast. Thus, it is difficult to employ these systems in practice.
Color formers which form a color by action of an acid are described in the literature "Chemistry of Functional Dye", R & D Report No. 13 CMC (1981), pp 189-206.
Other printing-out system is described, for example, in the literature "Light Sensitive Systems", J. Willey and Sons, New York (1955), pp 358-401 (written by J. Kosar, et al.).
Further, many examples of incorporating a printingout system in a photopolymerization system are known. Examples thereof include leuco color formers described in Japanese Patent Provisional Publication No. 60(1985)-163041 and lactone color formers described in Japanese Patent Provisional Publication Nos. 51(1976)-29137, 52(1977)-130701 and 55(1980)-13780.
However, these known color formers have disadvantages in that their solubility in a solution containing a polymerizable composition is low and the storage stability of solutions containing said known color former and the photopolymerizable composition is poor. Further, the known color formers have problems in that they are apt to lower the sensitivity of the photopolymerizable composition and as a result, the color density obtained after exposure decreases. Accordingly, the known color formers have a problem in practical use together with the photopolymerizable composition.